Alert micturator N brought this to my attention from the xkcd blag (no, it's not a blog, and this is not a blig), although I suppose it's something that men just know: If everybody uses the urinal farthest away from anybody else using one, some number of urinals (assuming they are all in a row) fill up (sic) more efficiently than others, also assuming that nobody will use the urinal directly adjacent to another pisher. Otherwise, apparently, Interolerable Awkwardness ensues.
While pondering the mathematics of this (sample factoid: there's a mens room at Fenway park that has 29 urinals and not a single mirror) I realized that similar behavior happens on subway cars, at least subway cars that are not already packed to the gills and subway cars that have rows of seats with some demarcation, rather than unmarked benches. (Don't get me started on the disconnect between the size of the average subway seat and the average American butt..) Anyway, most people try to sit such that they are not rubbing elbows (or other parts) with strangers, and even though a one-seat border zone is probably sufficient, most folks will sit as close to the middle of an empty stretch of seating as possible. Especially those who like to give their bags their own seats and those who prefer what I'll call a wider stance when sitting on the train. You know who you are.
If there are three seats open between two fellow travelers, the choice is clear, you sit in the middle. If there are just two, you either sit next to one or the other person or just stand. Four empties are about the same as three, but when there are five empty seats between people, things get interesting. (These calculations of course ignore the seats marked for handicapped people, just like the rest of the riders do)
X _ _ _ _ _ X 1 2 3 4 5 6 7
Well, if you want maximum lebensraum, you'll sit at spot 4, but that creates two patches of two empties each, and makes it impossible for anybody else to sit without being next to somebody.
X _ _ Y _ _ X 1 2 3 4 5 6 7
It would be more public-spirited to sit at 3 or 5, allowing more more person to sit at 5 or 3 and still maintain alternating buffer zones.
X _ Y _ z _ X 1 2 3 4 5 6 7
So if you happen to ride the train at an hour or direction that gives any choice of seating at all, consider if your seat selection maximizes space or awkwardness.